The short answer to your question is, we"d normally consider the use you outline below to require a proprietary license for Berkeley DB. If a third party writes an application that links the COBOL ISAM library, then that app is using Berkeley DB; it would have to be available in open source form, or would need a paid proprietary license.
However, there is not much business advantage to Sleepycat in requiring that this specific case adhere to the terms of our public license. The amount of money we"d make from users building COBOL ISAM apps would be small. Most likely, we"d simply drive people away from our software.
As a result, Sleepycat is willing to permit use of these COBOL libraries, including Berkeley DB, in proprietary or open source apps at no charge. We"re able to write you a variance letter that makes that explicit if you like.

April 7, 2005
Insider Hints at GPL Changes
By Michael Singer

Version 3.0 of the General Public License (GPL) may be years away, but one insider says proposed changes to it could impact companies like Amazon, Yahoo and Google.